• Posted April 24, 2023

Digestive Organs Vary Widely Between People, Study Finds

People are often reminded that they are their own unique person -- and a new study says that's particularly true of the digestive tract.

Dissections of a few dozen deceased individuals revealed striking differences in gastrointestinal anatomy, even among a small group of people.

Some livers were larger, some intestines and colons were longer. Crucial discrepancies were observed between men and women.

And some organs were even located in the wrong place, the researchers said.

"I almost missed one guy's appendix because it was growing off the back of the cecum [the pouch that forms the first part of the large intestine] instead of the front,"said lead researcher Erin McKenney, an assistant professor of applied ecology at North Carolina State University in Raleigh. "If I hadn't flipped it over and looked in the least likely spot, I would have missed it entirely."

These variations in anatomy have powerful implications for doctors and patients, the researchers said.

Surgery, medical treatments, and even lifestyle choices like diet, are often crafted to best serve an "average"person, but individual human digestive systems are far from average, the study found.

"If you're talking to four different people, odds are good that all of them have different guts, in terms of the relative sizes of the organs that make up that system,"McKenney explained.

Understanding the anatomical differences between people, and the health implications of those differences, could open up an entirely new field of personalized medicine.

"Given that there is more variation in human gut anatomy than we thought, this could inform our understanding of what is driving a range of health-related issues and how we treat them,"McKenney said.

Pediatric gastroenterologist Dr. Geoffrey Preidis agreed, saying that the new study "really raises a number of important points that should be addressed in future research."He is an assistant professor with Baylor College of Medicine and a scientific advisory board member with the American Gastroenterological Association's Center for Gut Microbiome Research and Education.

"For example, there is a chance that different sizes of various regions of the gastrointestinal tract could contribute to who is at risk for developing gastrointestinal disorders like irritable bowel syndrome versus who may be protected,"Preidis said.

The anatomy of the digestive system plays a crucial role in nutrition and health, but the last attempt to evaluate variations in the human gut occurred back in the 19^th century, McKenney noted.

Different guts, different health issues?

"The last study that really quantified and investigated variation in humans was published in 1885,"McKenney said. "For all of the technological advances and how amazing and individualized medicine is, we actually might also benefit from going back to square one and learning more about our bodies before we try applying all the technological Band-Aids."

To that end, McKenney and her colleagues dissected and measured the digestive organs of 45 people who donated their remains to the Anatomical Gifts Program at Duke University School of Medicine.

The investigators quickly learned that each person's guts varied significantly.

Take the cecum, a pouch that receives undigested food from the small intestine and is considered the beginning of the large intestine (colon).

"I always talk about the cecum as the 'wonder pouch' in between the small intestine and the large intestine. That's where stuff really slows down and gut microbes get a chance to start really fermenting,"McKenney said.

"The diagrams would have you believe that a typical cecum is going to be 1 to 2 inches, like a small pouch, a very modest size,"McKenney continued. "But one woman had a cecum 4 or 5 inches long. It was like a coin purse, you know. I was jealous of her cecum."

The researchers also found that women tend to have longer small intestines than men, while men have longer colons than women. The new study was published April 24 in the journal PeerJ.

This discovery supports the hypothesis that women are better able to survive periods where food is scarce, because they could be more capable than men of extracting nutrients from whatever fare is available, said Amanda Hale, who contributed to the research as a forensics laboratory manager at North Carolina State.

"A longer small intestine means generally more time to obtain any nutrients during digestion,"said Hale, now a forensic anthropologist with the Defense POW/MIA Accounting Agency. "You release bile into the early part of the small intestine, and so you have extra time to have additional uptake of nutrients from digestion."

Preidis explained that "in periods of fasting or famine or nutrient scarcity, theoretically, a longer small intestine -- and this is the region of the gastrointestinal tract that absorbs the bulk of the diet and in particular the fat from the diet -- could help buffer against some severe environmental stresses."

On the other hand, a longer colon implies that high fiber intake might be more important for the digestive health of men.

"If a person does not consume enough fiber to prevent constipation, then the longer the content sits in the lower gut, the more water is absorbed and the more impacted the feces might become,"McKenney noted.

"However, if a person is consuming sufficient fiber and complex carbohydrates to support microbial fermentation, then a longer colon would support both increased time for microbial fermentation and increase the opportunity for the body to absorb those beneficial fermentation products,"she continued.

Even mood might be affected

A larger colon also "could potentially contain a larger community of bacteria,"which might influence a person's susceptibility to gastrointestinal illnesses, Preidis said.

These variations are obviously important when it comes to surgery, particularly if a person's appendix isn't where it ought to be or one part of the intestinal tract is shorter than expected.

But the differences also could play a role in each person's risk of different digestive diseases, Hale said.

This study "highlights the need to investigate variation more in clinical medicine in terms of identifying an approach or identifying consistent patterns of variation in certain gastrointestinal illnesses,"Hale said.

People might be healthier if they altered their diet to reflect the individual differences of their own gut, McKenney and Hale said.

"I think it could be empowering for individual patients to consider that, like, I might be different, it might not be in my head. I could pay attention to how my body feels because maybe I'm just a different human,"McKenney said. "I think there's power in that."

There's even a chance that a person's mood and overall happiness could be linked to their specific digestive anatomy.

"Given everything that is coming out about probiotics -- specific beneficial microbes being tied to alleviating anxiety or depression or being associated with better moods or a feeling of well-being -- a longer gut could amplify those benefits,"McKenney said.

Given these potential benefits, McKenney and Hale think more research needs to be done on how variations in anatomy could affect a person's digestive health.

"Is there a way to prescribe a different approach to digestive health that's more suitable to a person's variation? For example, can we look at how alterations in diet may be more beneficial for one person's gut design than another's?"Hale asked.

"This could be important for both treatment and preventive medicine, but I also think we're a long way from identifying where that's helpful,"she concluded.

Preidus agreed that more research is needed.

"All of these hypotheses will need to be tested in future research, and I also want to be very clear that none of these very interesting findings have yet highlighted a causal link between any of these structural changes and the development or protection from human disease,"Preidus noted.

More information

The U.S. National Institutes of Health has more about the digestive tract.

SOURCES: Erin McKenney, PhD, assistant professor, applied ecology, North Carolina State University, Raleigh, N.C.; Amanda Hale, PhD, forensic anthropologist, Defense POW/MIA Accounting Agency; Geoffrey Preidis, MD, PhD, assistant professor, Baylor College of Medicine, Houston; PeerJ, April 24, 2023